S
Sean_Reid
Guest
Give Steve Gandy a call, and show him these pictures. It might be worth trying a second copy of the lens. There were reports of variations in performance with the CV21 and Cv25s. Ideally, the plane of sharpest focus should be a plane, not a sphere or other curved surface, but few lenses can really pull that off. Those that can are usually labeled macro lenses, and have been designed for flatness of field. When Sean shoots his resolution tests, he first checks very carefully to ensure that the back of the camera is parallel to the test wall, then focus brackets. I think he chooses the image which is sharpest in the center to study. If the image field is curved, then you will see that the corners are soft when the center is sharp.
scott
That's right. The camera must be absolutely parallel (horizontally and vertically) to the (nearly flat) test subject. Then one needs to focus bracket in steps so small that they, initially, do not even move the RF window. As Scott knows, as an engineering professor, one must eliminate confounding variables in order to see a set of results clearly. I strongly recommend that people not worry too much about results that "seem" to be revealed by casual testing. The method often just isn't precise enough to tell us what we need.
Cheers,
Sean